Warpage angle measurement apparatus and warpage angle measurement method for optical recording medium

ABSTRACT

A warpage angle measurement apparatus and a warpage angle measurement method are provided that can measure an angle of warpage of an optical disc and a cartridge for the optical disc caused by a rapid environmental change such as a temperature change or a humidity change in a short time. The warpage angle measurement apparatus  10  includes: a constant temperature chamber  22  for accommodating an optical recording medium  20  formed by mounting the optical disc  16  as an object to be measured in the cartridge  18  and for adjusting a surrounding of the optical recording medium  20  to have a predetermined environmental condition; a laser oscillator  24  for causing laser oscillation to emit laser light to the optical disc  16 ; and a light-receiving unit  26  for receiving the laser light reflected from the optical disc  16  and detecting a relative angle of an optical path L 2  of the reflected laser light with respect to an optical path L 1  of the emitted laser light.

TECHNICAL FIELD

The present invention relates to a warpage angle measurement apparatusand a warpage angle measurement method for measuring an angle of warpageof an optical disc and a cartridge for the optical disc.

BACKGROUND ART

Shortening of the wavelength of laser light and increasing of thenumerical aperture NA of an objective lens can increase recordingdensity and recording capacity in an optical disc. On the other hand, asthe wavelength of the laser light is shorter and the numerical apertureof the objective lens is larger, there is a tendency that comaaberration is generated and reduces accuracy of recording andreproducing information. However, margin for tilt (warpage) of theoptical disc can be ensured by making a light-transmitting layer of theoptical disc thin, thus ensuring the accuracy of recording andreproducing information.

In recent years, an optical disc has attracted attention, in whichblue-violet laser light having a wavelength as short as about 405 nm isused and numerical aperture NA is increased up to about 0.85 in order tolargely increase the recording capacity. A light-transmitting layerhaving a thickness of about 0.1 mm that is thinner than a substratehaving a thickness of about 1.1 mm is formed in accordance with theabove wavelength and NA (see Japanese Patent Laid-Open Publication No.2003-85836, for example).

This type of optical disc has high recording density and therefore theaccuracy of recording and reproducing information is easily affected bydust, scar, or the like. Thus, a cartridge in the form of a thin box isprepared. The cartridge has an opening for transmitting informationto/from the optical disc. The optical disc can be used in recordingand/or reproduction equipment while being mounted on the cartridge.Moreover, another type of cartridge that has the opening fortransmitting information and another opening for allowing printing to bepreformed on the optical disc and/or allowing the optical disc to beremoved and inserted therethrough.

In this type of optical disc, the numerical aperture NA of the objectivelens is increased up to about 0.85 as described above, and a distancebetween the objective lens and the optical disc is shortened inaccordance with the increased NA, as compared with a conventionaloptical disc such as CD (Compact Disc) and DVD (Digital Versatile Disc).Thus, there is a tendency that warpage causes interference between theoptical disc and the objective lens more easily in this type of opticaldisc than in the conventional optical disc, even if the degree of thewarpage is the same.

This type of optical disc is manufactured by forming alight-transmitting layer by spin coating on a substrate formed byinjection molding, for example. Thus, the substrate and thelight-transmitting layer are different in thickness and manufacturingmethod, and are sometimes different in material. Therefore, this type ofoptical disc has a problem that warpage can easily occur with a rapidchange in a temperature or a humidity.

For example, when an optical disc that is placed in an outdoor locationin winter and is therefore cooled down to a temperature close to anoutside air temperature is mounted on a video camera or the like that isheated by being turned on, an environmental temperature of the opticaldisc increases by several tens of degrees C. in several seconds andwarpage may occur. Moreover, when an optical disc that is placed in anoutdoor location in summer and is therefore heated to a temperatureclose to an outside air temperature is mounted on a recording andreproduction device or the like that is placed and cooled in anair-conditioned room, an environmental temperature of the optical disclowers by several tens of degrees C. in several seconds and warpage mayoccur. Large warpage can easily cause an error in reading andreproduction of information. Therefore, an angle of warpage should besuppressed within a predetermined limit value.

It is possible to suppress the angle of warpage within the predeterminedlimit value by making various improvements, for example, forming a layerhaving a coefficient of linear expansion equal to that of thelight-transmitting layer on an opposite surface of the substrate to thelight-transmitting layer.

However, even in the case where the warpage of the optical disc only issuppressed within the predetermined limit value, when that optical discis mounted in the cartridge, warpage exceeding the predetermined limitvalue may occur in the optical disc in the cartridge or warpage of thecartridge may occur. That warpage may cause an error in reading andreproduction of information.

In order to develop a highly reliable optical recording medium in whichthe angle of warpage of the optical disc and the cartridge issuppressed, it is important to quantitatively understand the angle ofwarpage caused by a rapid temperature change or a rapid humidity changeof the optical disc mounted in the cartridge or the cartridge thatoccurs in a short time.

However, in the conventional optical disc such as CD and DVD, thenumerical aperture of the objective lens is small and there is asufficient distance between the optical disc and the objective lens.Thus, warpage caused by a rapid temperature change or a rapid humiditychange in a short time does not become a problem. Therefore, there is nomethod for measuring an angle of warpage of an optical recording mediumcaused by a rapid temperature change or a rapid humidity changeoccurring in a short time.

Moreover, there is no method for measuring an angle of warpage of anoptical disc while the optical disc is mounted in a cartridge.

DISCLOSURE OF THE INVENTION

In view of the foregoing problems, various exemplary embodiments of thisinvention provide a warpage angle measurement apparatus and a warpageangle measurement method for an optical recording medium, which canmeasure an angle of warpage of an optical disc and a cartridge for theoptical disc that is caused by a rapid temperature change or a rapidhumidity change in a short time.

According to the present invention, at least one of an optical disc anda cartridge for the optical disc is accommodated as an object to bemeasured in a constant temperature chamber, a surrounding of the objectto be measured is adjusted to have a predetermined environmentalcondition, and an angle of warpage of the object to be measured ismeasured by emitting laser light to the object to be measured, receivingthe laser light reflected from the object to be measured, and detectinga relative angle of an optical path of the reflected laser light withrespect to an optical path of the emitted laser light. Thereby, theproblems described above can be solved.

The object to be measured may be accommodated in one constanttemperature chamber and the environmental condition may be rapidlychanged. Alternatively, two constant temperature chambers may be usedand environmental conditions inside those constant temperature chambersmay be set to be different from each other. In this case, when theobject to be measured is first placed in one of the two constanttemperature chambers and is then carried into the other constanttemperature chamber, it is possible to rapidly change the environmentalcondition of the optical disc in a short time and measure the angle ofwarpage of the object to be measured.

In summary, the above-described objectives are achieved by the followingaspects of embodiments.

(1) A warpage angle measurement apparatus comprising:

a constant temperature chamber for accommodating at least one of anoptical disc and a cartridge for the optical disc as an object to bemeasured and adjusting a surrounding of the object to be measured tohave a predetermined environmental condition; a laser transmitter forcausing laser oscillation to emit laser light to the object to bemeasured; and a light-receiving unit for receiving the laser lightreflected from the object to be measured and detecting a relative angleof an optical path of the reflected laser light with respect to anoptical path of the emitted laser light.

(2) The warpage angle measurement apparatus according to (1), furthercomprising an arithmetic unit for calculating the relative angle of anoptical path of the reflected laser light with respect to an opticalpath of the emitted laser light based on a position on thelight-receiving unit at which the reflected laser light arrives.

(3) The warpage angle measurement apparatus according to (1) or (2),wherein the constant temperature chamber has a through hole for allowingthe laser light to pass therethrough, and the laser transmitter and thelight-receiving unit are arranged outside the constant temperaturechamber.

(4) The warpage angle measurement apparatus according to (3), whereinthe through hole of the constant temperature chamber is closed with alight-transmitting member.

(5) The warpage angle measurement apparatus according to any one of (1)to (4), further comprising a mounting posture adjusting mechanism forholding the optical disc and the cartridge in the constant temperaturechamber while the optical disc is mounted in the cartridge and foradjusting a mounting posture of the optical disc in the cartridge.

(6) The warpage angle measurement apparatus according to any one of (1)to (5), further comprising a rotating and driving mechanism for drivingthe optical disc to rotate.

(7) A warpage angle measurement method comprising: accommodating atleast one of an optical disc and a cartridge for the optical disc as anobject to be measured in a constant temperature chamber; adjusting aninside of the constant temperature chamber to have a predeterminedenvironmental condition; and measuring an angle of warpage of the objectto be measured by emitting laser light to the object to be measured,receiving the laser light reflected from the object to be measured, anddetecting a relative angle of an optical path of the reflected laserlight with respect to an optical path of the emitted laser light.

(8) The warpage angle measurement method according to (7), wherein athrough hole for allowing laser light to pass therethrough is providedin the constant temperature chamber so that the laser light is emittedfrom an outside of the constant temperature chamber to the object to bemeasured and the reflected laser light from the object to be measured isreceived in the outside of the constant temperature chamber.

(9) The warpage angle measurement method according to (8), wherein thethrough hole of the constant temperature chamber is closed with alight-transmitting member so that the angle of warpage of the object tobe measured is measured.

(10) The warpage angle measurement method according to any one of (7) to(9), wherein the optical disc and the cartridge are held in the constanttemperature chamber while the optical disc is mounted in the cartridge,and a mounting posture of the optical disc in the cartridge is adjustedto measure the angle of warpage of the optical disc.

(11) The warpage angle measurement method according to any one of (7) to(10), wherein the angle of warpage of the optical disc is measured whilethe optical disc is driven to rotate.

(12) The warpage angle measurement method according to any one of (7) to(11), wherein the laser light is emitted to the optical disc through anopening for transmitting information of the optical disc provided in thecartridge while the optical disc is mounted in the cartridge, and thereflected laser light from the optical disc is reflected to an outsideof the cartridge.

(13) The warpage angle measurement method according to any one of (7) to(11), wherein an opening for measurement is formed in the cartridge, thelaser light is emitted to the optical disc through the opening formeasurement while the optical disc is mounted in the cartridge, and thereflected laser light from the optical disc is reflected to an outsideof the cartridge.

(14) The warpage angle measurement method according to any one of (7) to(13), wherein two constant temperature chambers are prepared andenvironmental conditions inside the two constant temperature chambersare set to have a different environmental condition from each other, andthe object to be measured is first accommodated in one of the twoconstant temperature chambers and is then carried into the otherconstant temperature chamber and thereafter the angle of warpage of theobject to be measured is measured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view schematically showing an entirestructure of a warpage angle measurement apparatus for an opticalrecording medium according to a first exemplary embodiment of thepresent invention.

FIG. 2 is a bottom cross-sectional view, taken along the line II-II inFIG. 1.

FIG. 3 is a cross-sectional side view schematically showing an exampleof use of the warpage angle measurement apparatus.

FIG. 4 is an enlarged cross-sectional side view of a surface of anoptical disc during a measurement using the warpage angle measurementapparatus.

FIG. 5 is a cross-sectional side view schematically showing an entirestructure of a warpage angle measurement apparatus for an opticalrecording medium according to a second exemplary embodiment of thepresent invention.

FIG. 6 is a bottom cross-sectional view, taken along the line VI-VI inFIG. 5.

FIG. 7 is a cross-sectional side view schematically showing a warpageangle measurement method for an optical recording medium according to athird exemplary embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred exemplary embodiments of the present invention will now bedescribed in detail, with reference to the drawings.

As shown in FIG. 1, a warpage angle measurement apparatus 10 includes: aconstant temperature chamber 21 for accommodating an optical recordingmedium 20 in which an optical disc 16 as an object to be measured, whichhas a light-transmitting layer 14 thinner than a substrate 12, ismounted in a cartridge 18 so as to adjust the surrounding of the opticalrecording medium 20 to have a predetermined environmental condition; alaser oscillator 24 for causing laser oscillation to emit laser light tothe optical disc 16; and a light-receiving unit 26 for receiving thelaser light reflected from the optical disc 16 and detecting a relativeangle of an optical path L2 of the reflected laser light with respect toan optical path L1 of the emitted laser light.

The warpage angle measurement apparatus 10 also includes an arithmeticunit 27 for calculating the relative angle of the optical path L2 of thereflected laser light with respect to the optical path L1 of the emittedlaser light based on a position on the light-receiving unit 26 at whichthe reflected light arrives.

The warpage angle measurement apparatus 10 further includes a mountingposture adjusting mechanism 28 for holding the optical disc 16 and thecartridge 18 in the constant temperature chamber 21 while the opticaldisc 16 is mounted on the cartridge 18 and for adjusting a mountingposture of the optical disc 16 in the cartridge 18.

The optical disc 16 is a circular plate having a thickness ofapproximately 1.2 mm and an outer diameter of approximately 120 mm. Acentral hole 16A having an inner diameter of approximately 15 mm isformed in the optical disc 16. The substrate 12 has a thickness ofapproximately 1.1 mm and the light-transmitting layer 14 has a thicknessof approximately 0.1 mm.

The substrate 12 is formed from a resin such as polycarbonate byinjection molding. A fine concavity and a fine convexity (both notshown) serving as a pit, a groove, and the like for transmittinginformation are transferred onto a surface of the substrate 12 on thelight-transmitting layer 14 side. In general, the terms “pit” and“groove” are used to mean a concave portion used for transmittinginformation. However, in this description, those terms are used to meannot only the concave portion but also a convex portion, as long as thatconvex portion is formed for the purpose of transmitting information,for convenience.

A magnetic plate 29 is arranged on a surface of the substrate 12 that isopposite to the light-transmitting layer 14 around a center.

The light-transmitting layer 14 is formed from a light-transmittingresin that can be hardened by radiation such as ultraviolet rays orelectron beams. The light-transmitting layer 14 is formed by spreadingthe resin on the substrate 12 by spin coating or the like and thenhardening the resin by being irradiated with radiation. Alternatively,the light-transmitting layer 14 may be formed by bonding alight-transmitting film formed of polycarbonate or the like to thesubstrate 12.

A functional layer (not shown) is formed between the substrate 12 andthe light-transmitting layer 14. For example, when the disc is a ROM(Read Only Memory) type, a reflective layer is formed as the functionallayer. When the disc is an RW (Re-Writable) type, a reflective layer anda layer of a phase change material are formed.

The cartridge 18 is an approximately square thin box, as shown in FIG.2, and is closed on one side (an upper side in FIG. 2) in a thicknessdirection. A communication opening 18A used for transmitting informationof the optical disc 16 is provided on the other side in the thicknessdirection.

The constant temperature chamber 21 is an approximately box-like memberand includes a temperature adjusting device, a humidity adjustingdevice, or the like (not shown). An environmental condition such as atemperature or humidity inside the constant temperature chamber 21 isadjustable. The constant temperature chamber 21 is supported by a base34 via a supporting post 32. A gap is formed between a bottom plate 22Aof the constant temperature chamber 21 and the base 34.

The bottom plate 22A has a through hole 22B formed therein for allowinglaser light to pass therethrough. The through hole 22B is closed with alight-transmitting member 36 formed of glass, acrylic resins, or thelike. A placing portion 38 onto which the mounting posture adjustingmechanism 28 is to be placed is provided on a top surface of the bottomplate 22A.

The laser oscillator 24 is arranged outside the constant temperaturechamber 22 under the through hole 22B and is attached onto the base 34to emit laser light to the inside of the constant temperature chamber 21through the through hole 22B. The laser oscillator 24 is arranged insuch a manner that an angle of emission of the laser light isadjustable.

The light-receiving unit 26 is also arranged outside the constanttemperature chamber 21 under the through hole 22B. The light-receivingunit 26 includes a CCD device, for example, and can detect a position atwhich reflected light arrives.

The arithmetic unit 27 is connected to the light-receiving unit 26 bycable. The arithmetic unit 27 may be arranged near the light-receivingunit 26 or at a position away from the light-receiving unit 26 via alead wire or the like. Alternatively, an arithmetic unit that isseparate from the warpage angle measurement apparatus 10, e.g., ageneral computer may be used.

The mounting posture adjusting mechanism 28 includes: a base plate 40; aplurality of (six in the present exemplary embodiment) supportingcolumns 42 projecting upward from the base plate 40; an intermediateplate 44 supported at a portion near an intermediate level of thesupporting columns 42 in a vertical direction; a plurality of (four inthe present embodiment) screw members 46 that are screwed with theintermediate plate 44 and have tops projecting upward from theintermediate plate 44; and a rotating and driving mechanism 48 forholding the optical disc 16 and driving the optical disc 16 to rotate.

The base plate 40 is a plate-like member having such a shape that thebase plate 40 is freely fitted into the placing portion 38 of theconstant temperature chamber 21. A through hole 40A for allowing laserlight to pass therethrough is formed in the base plate 40 at a positionabove the through hole 22B of the constant temperature chamber 21.

The supporting column 42 is a round-bar member and is arranged to be incontact with or close to a side face of the cartridge 18, therebyholding the cartridge 18 from the side, as shown in FIG. 2.

The intermediate plate 44 has a through hole 44A for allowing laserlight to pass therethrough at a position above the through hole 40A ofthe base plate 40. The intermediate plate 44 also has screw holes 44Bwith which the screw members 46 are respectively screwed at fourlocations. The intermediate plate 44 further has a through hole 44C forthe rotating and driving mechanism 48 around a center thereof.

The screw members 46 are arranged in such a manner that they are incontact with a lower surface of the cartridge 18 near corners of thecartridge 18 and support the cartridge 18 from beneath. Positions of thetops of the four screw members 46 in the vertical direction are adjustedin an appropriate manner by rotating the screw members 46. In thismanner, it is possible to hold the cartridge 18 horizontally and adjustthe position at which the cartridge 18 is held in the vertical position.

The rotating and driving mechanism 48 includes a chuck member 50 forengaging with the central hole 16A of the optical disc 16; a shaftmember 52 for supporting the chuck member 50 from beneath; a shaftbearing member 54, attached to the base plate 40, for supporting theshaft member 52 to be freely rotatable; a gear 56 attached to the shaftmember 52; a pinion 58 that is to be in mesh engagement with the gear56; and a motor 60 for driving the pinion 58 to rotate.

The chuck member 50 is magnetized. The chuck member 50 is fitted intothe central hole 16A of the optical disc 16 and magnetically adheres tothe magnetic plate 29 of the optical recording medium 12, therebyholding the optical disc 16.

Next, a method for measuring an angle of warpage of the optical disc 16,that uses the warpage angle measurement apparatus 10, will be described.It is only necessary to prepare one mounting posture adjusting mechanism28, whereas two constant temperature chambers 21 are prepared.

First, an angle of laser emission of the laser oscillator 24 isadjusted. More specifically, a calibration disc is placed on the chuckmember 50 of the mounting posture adjusting mechanism 28. Thecalibration disc has the same outer diameter and shape as those of theoptical disc 16, has a central hole having an inner diameter of about 15mm, and is formed of glass. The calibration disc is accommodated in theconstant temperature chamber 21 together with the mounting postureadjusting mechanism 28. Then, laser light is emitted onto thecalibration disc, and the angle of laser emission of the laseroscillator 24 is adjusted so as to make an angle between emitted lightand reflected light 0°, i.e., make an optical path of the emitted lightcoincident with an optical path of the reflected light.

Subsequently, instead of the calibration disc, the optical recordingmedium 20 is mounted on the mounting posture adjusting mechanism 28. Inthis mounting, four screw members 46 are rotated in an appropriatemanner, thereby holding the cartridge 18 approximately horizontally andadjusting the held position of the cartridge 18 in the verticaldirection without bringing both sides of the optical disc 16 intocontact with the cartridge 18. This adjustment may be performed insidethe constant temperature chamber 21 or outside the constant temperaturechamber 21. After the adjustment of the mounting posture is completed,the optical recording medium 20 is detached from the mounting postureadjusting mechanism 28 once.

Two constant temperature chambers 22 are set to have differentenvironmental conditions from each other. For example, a temperatureinside one of the constant temperature chambers 22 is adjusted to a lowtemperature, while a temperature inside the other constant temperaturechamber 21 is adjusted to a high temperature.

Subsequently, the optical recording medium 20 is accommodated in one ofthe constant temperature chambers 22. Thus, the optical recording medium20 is rapidly heated (or cooled). Since the optical recording medium 20has the communication opening 18A on only one side of the cartridge 18,a temperature of a surface of the optical disc 16 on a side close to thecommunication opening 18A becomes close to a surrounding temperaturerelatively quickly and a temperature of an opposite surface becomesclose to the surrounding temperature late. In other words, a temperaturedistribution in the optical disc 16 temporarily becomes uneven in thethickness direction, thus causing warpage. However, a variation in thetemperature distribution in the optical disc 16 becomes smaller withtime and the warpage is gradually converged.

The optical recording medium 20 continues to be accommodated in oneconstant temperature chamber 21 until the temperature distribution inthe optical recording medium 20 becomes sufficiently even. After a stateof the optical recording medium 20 becomes stable, the optical recordingmedium 20 is taken out from that constant temperature chamber 21 and isthen mounted on the mounting posture adjusting mechanism 28 inside thesecond temperature chamber 25 as shown in FIG. 3. Thus, the opticalrecording medium 20 is rapidly cooled (or heated) and the temperaturedistribution in the optical disc 16 temporarily becomes uneven in thethickness direction, thus causing warpage.

In this state, when laser light is emitted from the laser oscillator 24to a portion on the optical disc 16 near an outer circumference of theoptical disc 16 through the communication opening 18A of the cartridge18, the laser light is reflected by a surface of the optical disc 16.However, the surface of the optical disc 16 is inclined with respect tothe horizontal direction because of the warpage, as shown in FIG. 4 thatshows warpage in an enlarged view. Thus, the optical path L2 of thereflected light is slightly inclined with respect to the verticaldirection and is not coincident with the optical path L1 of the emittedlight.

The light-receiving unit 26 detects a position at which the reflectedlight arrives. The arithmetic unit 27 calculates an angle of the opticalpath L2 of the reflected light based on the position on thelight-receiving unit 26 at which the reflected light arrives, andmeasures an angle formed by the optical path L1 of the emitted light andthe optical path L2 of the reflected light as an angle of warpage α.Incidentally, assuming that an angle formed by a virtual surface of theoptical disc 16 and an actual surface that is measured is θ in the casewhere no warpage occurs, α and θ satisfy the relationship of α=2θ.

The angle of warpage α may be measured while the optical disc 16 isrotated by means of the rotating and driving mechanism 48. In this case,an average angle of warpage in a circumferential direction, a variationin the angle of warpage in the circumferential direction, and the likecan be measured.

Incidentally, the variation in the temperature distribution in theoptical disc 16 becomes small with time and the warpage is graduallyconverged.

As described above, the warpage angle measurement apparatus 10 canmeasure the angle of warpage of the optical disc 16 while the opticalrecording medium 20 is accommodated in the constant temperature chamber21. Thus, it is possible to measure the angle of warpage of the opticaldisc 16 caused by a rapid change in the environmental condition such asa temperature occurring in a short time in real time. Therefore, thewarpage angle measurement apparatus 10 has high reliability.

Moreover, the warpage angle measurement apparatus 10 includes themounting posture adjusting mechanism 28, and can measure the angle ofwarpage of the optical disc 16 while the mounting posture of the opticaldisc 16 in the cartridge 18 is kept without bringing both sides of theoptical disc 16 into contact with the cartridge 18. Therefore, thewarpage angle measurement apparatus 10 has high measurement precision.In this regard, the reliability of the warpage angle measurementapparatus 10 is improved.

In addition, the warpage angle measurement apparatus 10 includes therotating and driving mechanism 48 and can measure the angle of warpageof the optical disc 16 while rotating the optical disc 16. Therefore,the warpage angle measurement apparatus 10 can perform variousmeasurements, e.g., a measurement in which a variation in the angle ofwarpage in the circumferential direction is considered.

Since the laser oscillator 24 and the light-receiving unit 26 arearranged outside the constant temperature chamber 22 in the warpageangle measurement apparatus 10, the laser oscillator 24 and thelight-receiving unit 26 are not excessively heated or cooled. In thisregard, the warpage angle measurement apparatus 10 has high measurementprecision and improved reliability.

In the warpage angle measurement apparatus 10, the through hole 22B ofthe constant temperature chamber 21 is closed with thelight-transmitting member 36 and can be air-tightly sealed from theoutside. Therefore, heating efficiency and cooling efficiency are goodand the environmental condition can be quickly adjusted.

Since laser light is emitted to the optical disc 16 by using thecommunication opening 18A of the cartridge 18, preparation for themeasurement, such as processing of the optical recording medium 20, isnot required. Therefore, it is possible to easily perform themeasurement.

Next, a second exemplary embodiment of the present invention will bedescribed.

In the second exemplary embodiment, a cartridge 64 of an opticalrecording medium 62 includes a communication opening 64A and an opening64B for removal and insertion of an optical disc provided on theopposite side to the communication opening 64A, as shown in FIG. 5.Laser light is emitted to the optical disc 16 through the opening 64Bfor removal and insertion, thereby measuring an angle of warpage of theoptical disc 16.

More specifically, the opening 64B for removal and insertion has a shapeformed by an arc slightly larger than the optical disc 16 and a straightline near an end (left end in FIG. 6) of the arc, as shown in FIG. 6.The optical disc 16 can be inserted through the opening 64B for removaland insertion. The optical recording medium 62 is arranged to allow theoptical disc 16 to be taken out from the cartridge 64. Moreover,printing of a character, a drawing, and the like can be performed on theoptical disc 16 through the opening 64B for removal and insertion.

A warpage angle measurement apparatus 60 of the second exemplaryembodiment is different from the warpage angle measurement apparatus 10of the first exemplary embodiment in that a through hole 22D is formedin a top board 22C of the constant temperature chamber 21, the throughhole 22D is closed with the light-transmitting member 36, and the laseroscillator 24 and the light-receiving unit 26 are attached above thethrough hole 22D of the constant temperature chamber 21. No through holefor allowing laser light to pass therethrough is formed in each of thebase plate 40 and the intermediate plate 44 of the mounting postureadjusting mechanism 28. Except for the above, the structure of thewarpage angle measurement apparatus 60 is the same as that of theaforementioned warpage angle measurement apparatus 10. Therefore, thesame structure is labeled with the same reference numerals as those inFIGS. 1 and 2 and the description thereof is omitted. The method formeasuring an angle of warpage of the optical disc 16 is also omittedbecause it is the same as that in the first embodiment.

In the second exemplary embodiment, an angle of warpage of the opticaldisc 16 caused by a rapid environmental change such as a temperaturechange or a humidity change occurring in a short time can be measured inreal time, as in the first exemplary embodiment. Thus, high reliabilitycan be achieved.

Moreover, laser light is emitted to the optical disc 16 by using theopening 64B provided in the cartridge 64 for removal and insertion ofthe optical disc 16. Thus, preparation for the measurement, such asprocessing of the optical recording medium 62, is not required.Therefore, it is possible to easily perform the measurement.

Next, a third exemplary embodiment of the present invention will bedescribed.

In the first and second exemplary embodiments, laser light is emitted tothe optical disc 16 by using the communication opening 18A of thecartridge 18 and the opening 64B of the cartridge 64 provided forremoval and insertion of the optical disc 16, respectively. On the otherhand, in the third exemplary embodiment, an opening 18B for measurementis provided in the cartridge 18 and laser light is emitted to theoptical disc 16 through the opening 18B, as shown in FIG. 7.

In the third exemplary embodiment, the warpage angle measurementapparatus 60 of the second exemplary embodiment is used for measuringthe optical recording medium 10 of the first exemplary embodiment andthe opening 18B for measurement is formed in the cartridge 18. Exceptfor the above, the third exemplary embodiment is in common with thefirst and second exemplary embodiments. Therefore, the common componentsof the optical recording medium and the warpage angle measurementapparatus are labeled with the same reference numerals as those in FIGS.1, 2, and 5 and the description thereof is omitted. The method formeasuring an angle of warpage of the optical disc 16 is also the same asthat in the first embodiment and therefore the description thereof isomitted.

As described above, the opening 18B for measurement is provided in thecartridge 18. Thus, warpage of the optical disc can be measuredirrespective of the shape of the cartridge. Moreover, the warpage at adesired position of the optical disc can be measured.

In the first to third exemplary embodiments, the mounting postureadjusting mechanism 28 includes the rotating and driving mechanism 48.However, the present invention is not limited thereto. For example, inthe case where a variation in warpage of the optical disc in thecircumferential direction does not become a problem, the rotating anddriving mechanism may be omitted.

In the first to third exemplary embodiments, the mounting postureadjusting mechanism 28 includes the screw members 46, the supportingcolumns 42, and the like. However, the present invention is not limitedthereto. The structure of the mounting posture adjusting mechanism isnot specifically limited, as long as it can adjust the mounting postureof the optical disc in the cartridge.

In the first to third exemplary embodiments, each of the warpage anglemeasurement apparatuses 10 and 60 includes the mounting postureadjusting mechanism 28 for adjusting the mounting posture of the opticaldisc 16 in the cartridge 18 or 64 in the constant temperature chamber21. However, the present invention is not limited thereto. In the casewhere an effect of contact of the optical disc and the cartridge witheach other on the angle of warpage of the optical disc can be ignored,no mounting posture adjusting mechanism may be provided. In this case,the angle of warpage of the optical disc may be measured while only oneof the optical disc and the cartridge is held, for example.

In the first to third exemplary embodiments, the through holes 22B and22D of the constant temperature chamber 21 are closed with thelight-transmitting member 36. However, the present invention is notlimited thereto. For example, in the case where the constant temperaturechamber 21 has sufficient heating and cooling capabilities and it ispossible to adjust the environmental condition inside the constanttemperature chamber 21 even when the through holes 22B and 22D areopened, the light-transmitting member 36 may be omitted and the throughholes 22B and 22D may be opened.

In the first to third exemplary embodiments, the temperature is adjustedas the environmental condition inside the constant temperature chamber21. However, the present invention is not limited thereto. For example,another environmental condition such as a humidity may be adjusted so asto measure the angle of warpage of the optical disc.

In the first to third exemplary embodiments, the laser oscillator 24 andthe light-receiving unit 26 are arranged outside the constanttemperature chamber 21. However, the present invention is not limitedthereto. For example, in the case where a range within which thetemperature inside the constant temperature chamber 21 can be adjustedis close to a room temperature and the optical disc is not rapidlyheated or cooled even when being placed in the constant temperaturechamber 21, the laser oscillator 24 and the light-receiving unit 26 canbe arranged inside the constant temperature chamber 21. In this case,the constant temperature chamber 22 may have a structure in which thethrough holes 22B and 22D are omitted.

In the first to third exemplary embodiments, two constant temperaturechambers 21 are prepared, the temperatures in those constant temperaturechambers 21 are set to be different from each other, the opticalrecording medium 20 (62) is accommodated in one of the constanttemperature chamber 21 and is then carried into the other constanttemperature chamber 21, and thereafter the angle of warpage of theoptical disc 16 is measured. However, the present invention is notlimited thereto. For example, in the case of measuring the angle ofwarpage occurring when the temperature is changed from the roomtemperature to a high temperature or a low temperature, only oneconstant temperature chamber 21 may be prepared, the inside of theconstant temperature chamber 21 may be adjusted to a temperaturedifferent from the room temperature, the optical recording medium 20(62) may be carried into the constant temperature chamber 21 after beingleft in the environment of the room temperature outside the constanttemperature chamber 21, and then the angle of warpage of the opticaldisc 16 may be measured.

In the first to third exemplary embodiments, the angle of warpage of theoptical disc 16 mounted on the cartridge 18 (64) is measured. However,the present invention is not limited thereto. It is possible to measurean angle of warpage of an optical disc itself caused by a rapidtemperature change or a rapid humidity change in a short time, while theoptical disc is not mounted in the cartridge.

In the first to third exemplary embodiments, the optical disc 16 havingthe light-transmitting layer 14 thinner than the substrate 12 is anobject to be measured. However, the present invention is not limitedthereto. It is also possible to measure an angle of warpage caused by arapid temperature change or a rapid humidity change in a short time foranother type of optical disc such as DVD in which a substrate and alight-transmitting layer have the same thickness and CD in which asubstrate serves as a light-transmitting layer.

In the first to third exemplary embodiments, the angle of warpage of theoptical disc 16 is measured. However, the present invention is notlimited thereto. An angle of warpage of a cartridge for an optical disccaused by a rapid temperature change or a rapid humidity change in ashort time can be also measured.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to measure an angleof warpage of an optical disc and a cartridge for the optical disccaused by a rapid change in a temperature or a humidity occurring in ashort time. Thus, the present invention can contribute to development ofa highly reliable optical recording medium in which warpage of theoptical disc and the cartridge for the optical disc can be suppressed.

1. A warpage angle measurement method comprising: accommodating at leastone of an optical disc and a cartridge for the optical disc as an objectto be measured in a first constant temperature chamber; adjusting aninside of the first constant temperature chamber to have a predeterminedenvironmental condition including at least one of a temperature and ahumidity; preparing a second constant temperature chamber, wherein theenvironmental conditions inside the first constant temperature chamberand the second constant temperature chamber are adjusted to have adifferent environmental condition from each other, and the object to bemeasured is first accommodated in the first constant temperature chamberand then carried into the second constant temperature chamber; andthereafter, measuring an angle of warpage of the object to be measuredby emitting laser light to the object to be measured, receiving thelaser light reflected from the object to be measured, and detecting arelative angle of an optical path of the reflected laser light withrespect to an optical path of the emitted laser light.
 2. The warpageangle measurement method according to claim 1, wherein the optical discand the cartridge are held in the first and second constant temperaturechambers while the optical disc is mounted in the cartridge, furthercomprising adjusting a mounting posture of the optical disc in theoptical disc for measuring of the angle of warpage of the optical disc.3. The warpage angle measurement method according to claim 1, whereinthe angle of warpage of the optical disc is measured while the opticaldisc is driven to rotate.
 4. The warpage angle measurement methodaccording to claim 1, wherein the laser light is emitted to the opticaldisc through an opening for transmitting information of the optical discprovided in the cartridge while the optical disc is mounted in thecartridge, and the reflected laser light from the optical disc isreflected to an outside of the cartridge.
 5. The warpage anglemeasurement method according to claim 1, wherein an opening formeasurement is formed in the cartridge, the laser light is emitted tothe optical disc through the opening for measurement while the opticaldisc is mounted in the cartridge, and the reflected laser light from theoptical disc is reflected to an outside of the cartridge.